


Revelations 21:6

by castiel_ambrose



Series: SPN Kinkmeme Fills [2]
Category: Supernatural
Genre: Alpha Dean Winchester, Alpha/Beta/Omega Dynamics, Angst, Beta Sam Winchester, Bottom Castiel, Dean has no condom oops, First Time, Fluff and Smut, M/M, Mating Cycles/In Heat, My First Smut, Omega Castiel, Omega Castiel/Alpha Dean Winchester, Really fluffy, Really small hint of angst, Smut, Top Dean Winchester, Unsafe Sex, somewhat slow burn
Language: English
Status: Completed
Published: 2018-06-16
Updated: 2018-06-16
Packaged: 2019-05-23 23:27:16
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,002
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14943323
Author URL: https://archiveofourown.org/users/castiel_ambrose/pseuds/castiel_ambrose
Summary: Filled for an SPN Kinkmeme prompt!Title inspired by the verse of the same name in the King James Version of the Bible.---Angels are Betas once they enter a vessel. That vessel, regardless of what it was, stays Beta for as long as the angel stays inside it. Castiel is a regular angel in that he's the same way. But soon, slowly, his body begins to change as a result of his and Dean's "profound bond", and it begins to shift into an Omega's body, which shouldn't even be possible.Castiel is left to piece together his purpose now while Dean tries to adjust to the idea of Castiel being an Omega, as well as possibly his mate.Until Castiel's first heat strikes, and they have to decide what will happen and where this leaves them.





	Revelations 21:6

**Author's Note:**

> Hey! This is my first time writing A/B/O, so I hope I did it fine! This was inspired by a prompt and I really enjoyed writing this.
> 
> Not beta'd, all mistakes are my own. That being said, I hope you enjoy!

****It was a hint of a whiff, at first. Castiel brushed past Dean in the library, looking for a book, and Dean smelled it. Ever since Dean knew him, the angel had the now familiar scent of the sky that was about to rain. It had always had the Beta characteristic of being watered down, almost unappealing.

But it was different, this time. Now, it made Dean’s blood heat for a second, made his eyes widen marginally, called to him faintly and distantly. But as soon as he turned to the angel, the scent was gone, and he was left with normalcy. Castiel was too absorbed in his task to talk, and Dean didn’t think to push or question.

* * *

 “Maybe you’re horny and really desperate.” Was Sam’s reply, not even looking up from his laptop. Castiel wasn’t around, for once, and Dean had confided in his brother what had happened a few days prior. Dean rolled his eyes; he hadn’t expected sympathy or even an actual answer, but one of those two might’ve been nice.

“It’s not that, Sam. It was just… strong. Like it was his scent, but it was laced with something. Is it like… a Beta thing?” Sam was one of the few Betas that Dean knew, aside from Castiel.

Sam sighed. “Not that I know. I’ve never heard of anything like that happening.” Betas were designed to be unappealing to most, naturally, so they could not only keep the balance between Alphas and Omegas but lead them to -- hopefully -- better matings. There were plenty of Betas with mates, however.

It didn’t help Dean, much. He gave something between a sigh and a groan and sat back in his chair. About a hundred thoughts were running through his head, and he didn’t know why. A few minutes passed, only filled by the tapping of Sam’s laptop keys before it stopped.

“Dean? Come look at this.”

“Hmm?” Dean got up and sat next to Sam. “ _How To Know My Secondary Gender_? How the hell did you find this?”

“Popped up on Google while I was searching around. But look here, on what it says about presenting.”

“Scent becomes one of the few signs, everyone knows that. Then demeanor…” Dean’s eyes skimmed the page, going over information that you learn in high school biology until one little blurb made him stop.

_An unmated Omega’s scents are specifically meant to draw in potential mates. They intensify around potential mates they find suitable, sweeter and stronger than others they give off._

“Omega? No, Cas is a Beta, isn’t he? That’s what he said angels are. Cas doesn’t even act like an Omega.”

Angels had no set gender of any kind. When they inhabited a vessel, regardless of what that vessel was before, it became a Beta, unless the angel changed it back when they left.

“I’m not saying he is, but it’s something to consider.”

“What’s to consider?” Castiel walked into the war room, and Dean nearly jumped out of his skin as he turned to face him. Sam’s laptop, thankfully, was faced the other way.

“Don’t just walk into a room, Cas. We talked about this.”

“I’m sorry.” It was difficult to tell if he was actually sorry, or if he was just appeasing Dean on something he really didn’t need to be on edge about. “But what’s to consider?”

“A case,” Sam spoke up. “It looks like it might pan out.”

“We should go, then,” Castiel suggested, and walked past Dean again, hitting his nostrils with that same scent and making his grip on Sam’s chair tighten. If it was going to be a few days of this, Dean didn’t know if he would make it back to the Bunker alive.

* * *

 Sam did manage to scrounge together a case, which was simple enough that they were home within a few days. Instead of being disappointed, Dean took the extra time to look up more on Omegas; presenting, biology, and even -- Dean tried to not get too worked up -- mating processes. Dean had never grown up with a permanent Omega in his life and wasn’t around long enough to know Omegas who were presenting in his adolescence.

He also took the time to study Castiel, really study him, and compared it to what he knew. Of course, he couldn’t tell some of the things that apparently went with an Omega, such as widening hips. But he could see other things. He could see the way Castiel unconsciously stood closer to Dean, and not too aggressively either. He saw the way Castiel’s eyes wouldn’t meet those of an Alpha he wasn’t familiar with, at least for a quick second. And he saw it when Castiel walked by Sam one day, and the younger Winchester nearly dropped his sandwich for a second. All of them were quick, instinctual, but Dean had a good inkling of what was what. Castiel was turning into an Omega.

Either the angel was oblivious, or brushed it off and justified it with other reasons. The brothers didn’t say anything about it, which wasn’t good, but they didn’t know how to exactly approach the topic until it was shoved on top of them. It was almost stupid how it happened.

“Would you like to try some scented lotion? It’s specifically designed to act as a soothing agent for stressed Omegas.”

The preppy girl’s voice hit Dean an aisle over and he froze like a statue, even his hand stopping as he reached for the shampoo. The Bunker had been running low on supplies, so Dean had made a rare stop at a store for a refill. Castiel had wanted to come with, which Dean figured meant he wanted a few new books or a DVD. In hindsight, Dean knew he should’ve known something was going to happen. He held his breath and listened further.

“That’s very kind, but no thank you.”

“Are you sure? It’s all organic. And I’m sure you and your Alpha would appreciate it during your heats, or-”

“I’m not mated. And I’m a Beta. So, thank you, but no thank you.” Castiel’s voice was polite but short. The associate’s turned confused.

“You don’t _smell_ Beta.” Then there was a soft “oh” and an understanding tone. “You don’t have to pretend. I promise I won’t judge. Omegas stick together, after all.”

There was a pause, long and almost painful. Then there was a quiet “excuse me”, and Dean heard dress shoes walking away with purpose and no small amount of anger. They receded and the door distantly beeped as someone left the store. Dean swallowed and quickly finished shopping. Castiel would be waiting in the Impala, and Dean almost dreaded what would happen. Would he get stony silence and a scent of betrayal filling his car? Or would it be fiery anger and heated words on the drive back? Dean had been on the receiving end of both, though only enough that he could count on one hand how many times either had happened. He wasn’t sure if he preferred one over the other.

Castiel was facing forward in the passenger seat, and through the windshield, Dean could tell the familiar angelic look of being wholly pissed. His jaw was set and the blue eyes didn’t even meet Dean, resolutely avoiding him out of some sort of spite. Dean took his time putting the plastic bag in the backseat before he slipped into the driver’s seat. The Alpha hesitated before he spoke.

“Cas, I-”

“Just drive, Dean.” The ice in his voice conflicted with the heat in his eyes.

And for once, Dean shut up and obeyed.

* * *

“You both knew, didn’t you?” Castiel asked Sam and Dean as Dean followed him into the Bunker.

“Knew what?” Sam asked.

“That I was an Omega, Sam. Don’t act as if you didn’t know.” Castiel had been quiet for the whole car ride, biding his time and anger until he could properly release it on the both of them.

At Sam’s wide-eyed look, Dean spoke up and explained. “A spokesperson offered him something for Omega use and said he didn’t smell like Beta. So…”

“How long have you two known?” Castiel interrupted.

“I don’t know… About two weeks.”

“I smelled it.” Dean cut in, turning pink slightly. “We didn’t tell you what was happening because we weren’t entirely sure.” It wasn’t a lie, not totally.

The betrayed look on Castiel’s face didn’t fade, and neither did the anger, but instead of blowing up, he stayed silent.

“Cas…” Sam started up quietly, trying to find the words to say. “It’s fine. You’ll-”

Finally, Castiel made a move and quickly turned on his heel, going up the stairs with heavy footsteps. He smelled sour, Dean noted, but alongside the anger, there was another scent; tamer, but no less impactful. It was almost sad. Dean barely waited two minutes before he found himself in front of Castiel’s room, knocking on the door.

“Cas? Are you there?” He asked through the door. There was a pause for a minute before Cas opened his door, anger on his face but diminished.

“Have you come to apologize?”

“No- Well, yeah. Sort of.” Dean looked down and wet his lips quickly before he looked back up at Castiel. “Can I come in?”

Dean thought he would get a rejection, but Cas silently moved to the side and opened the door more to let the Hunter enter. That gave Dean hope, at least a bit. Walking into the room, he did smell more of Castiel, surrounding him. Castiel never slept in here or even stayed in here much, but there was still a faint smell in the air.

“Why didn’t you tell me?” Castiel asked, turning Dean’s attention back to the Omega.

“We… I didn’t know what was happening. I thought it was a Beta thing… I didn’t think it could happen to turn you Omega.”

“It should be impossible, you’re right.” Castiel was quiet. “It’s never happened to any angel.”

“It doesn’t make you any different, Cas.” Dean stepped towards the angel, trying to offer any words of comfort he could. Castiel flinched slightly.

“How does it not make things different, Dean? My whole purpose has been changed…” Castiel said. “I’m different, now.”

“You’re still Castiel.”

“I’m an Omega, now. What do Omegas do, Dean? I see how they’re treated by humankind. At least as a Beta, I had some power.” The inflection in his words made Dean flinch this time, knowing what Castiel meant.

For all the rights Omegas had gained in the past few decades, they could be unfairly discriminated against, legally in some places. Employment could be limited, they could be forced to be mated, and Alphas had total control over them in a few states. They were the “weaker” gender. That’s what had been instilled in Dean. And it was what was instilled in many Omegas and even Betas.

“It’s not the same now, Cas. And if you think we’ll let anyone else treat you like that… then you don’t have a lot of faith.” That was what Dean knew was true. And it was what he thought Castiel needed to hear.

The Omega looked only partially satisfied, but his shoulders dropped marginally, the tension ebbing away. Suddenly, he looked two feet smaller.

“I want to believe you.”

“You can. Trust me.”

He was silent for a few minutes before he finally looked up, eyes meeting Dean’s.

“I do.”

* * *

 The next week after the conversation went well enough. It was mostly a large adjustment stage, after that. Sam had a similar talk with Castiel, confirming everything Dean had said. It wasn’t smooth sailing, but as Castiel allowed the Alpha and Beta back in, it got a bit better with each day. The transition even seemed to go a bit faster, and Dean made sure to pass on what he had learned in the past two weeks to the angel, and in return the angel’s body seemed to just produce more of the heated scent that seemed to settle sweetly in Dean’s stomach, while riling him up. It was such a stereotypical Alpha response, but Dean attributed it to his biology and couldn’t stop it, no matter how much he wanted to.

It all came to a head one day when Dean heard a glass shatter in the kitchen. Soon after there was something that was equivalent to a groan, and Dean was quickly out of his chair to find out what had happened. Sam had left ten minutes ago, and Castiel was the only one left in the Bunker besides Dean.

His hope that Castiel wasn’t injured partially came to be true as he swung the door open. The Omega was huddled on the ground, curled up as he sat, hands wrapping around his stomach. There was glass shattered on the floor, and Dean maneuvered around it as best as he could before he crouched down next to Cas.

“Cas, what the Hell-” He was cut off at the scent. It was like everything else he had smelled so far multiplied by one hundred. And when Castiel looked up at him with an almost glazed look in his eyes, full of want and nearly brimming with tears, Dean felt an overwhelming urge to protect and hold close.

“I- I don’t…” He was cut off by another whine and lurched forward, shaking all over. “It hurts, Dean. I feel… hot.”

Dean immediately brought him closer, holding him and trying to calm the shivers wracking his body. The Alpha frantically tried to think through what was going on, because having a sick Omega in his arms and giving off desperate vibes wasn’t exactly ideal, despite the fact that it felt right like he was supposed to.

“Cas… Cas, listen to me.” He spoke quietly, still holding the Omega close. “I think you’re going through your first heat.” Dean knew there was supposed to be some sort of nesting ritual, but if Cas hadn’t known what or when to expect it, he couldn’t have prepared.

The angel pressed himself closer to Dean. If he heard Dean’s words, he made no mention of it. The hunter told him to brace himself quietly and picked the angel up like he was nothing, just to take him out of the glass and up to his room. He would clean it up later, but right now had other, more important things to attend to.

Once he got to Castiel’s room, he set him gently on the bed and tried to strip the coat off of Castiel’s and make him comfortable.

“Don’t go. Dean…” Cas curled in on himself and Dean was quickly there, next to him in bed.

“I’m not going anywhere, Cas. I was just taking care of your coat.” He rolled the other onto his back to get a better look at him and swallowed at the look in Castiel’s eyes. They were onyx black, pupils dilated to where there was only a sliver of an ocean blue ring of his eyes. He became acutely aware of how close he was to the angel, how sweet he really smelled, and what those eyes meant.

“I need you.”

“Cas, we-” Castiel leaned up and softly brushed his lips against Dean’s, making whatever Dean was going to say meaningless. He froze at how it felt, soft but chapped lips pushing up against his own; he would be lying if he said that he had never thought of this, of imagining just once how it would feel for the angel to take that next step, what it would lead to. But he never let himself have hope, and this was so much different than anything else he could’ve imagined.

“Please. I want you, Dean. I… I need an Alpha. I _need_ _you_.” Castiel said against his lips, and Dean couldn’t help but allow himself to feel the same. His Omega needed comfort, and he knew what that meant.

“You have me, Cas.” Was the only assurance he could get out before he was kissing him again, deeper but no less slow, or passionate. The Omega melted and Dean took the advantage to lean him down onto his back, kisses trailing down to his neck as Castiel’s hands fisted in Dean’s hair.

“It’s alright, I’m not going anywhere. But I have to get you out of your clothes.” As he soothed the harried Omega, his fingers loosened the tie and unbuttoned the white dress shirt that clung to his torso out of sweat. Even with his body’s transitioning, he still had sculpted muscles and a mile of tanned skin. Dean couldn’t help but admire it, actually allowing let himself get close enough to feel it all.

“Beautiful.” He murmured, not even thinking as he took his own shirt off. The Omega turned pink, but the shaky breath he let out at the words was intensified as Dean took off the rest of his clothes until he was left in his boxers, hands reaching out to feel and grab, just for sake of contact. His erection was straining against the fabric, and even the loose and worn cotton didn’t help. But he shouldered it, not wanting to shuck them off just yet until Castiel was sure. He wanted to make this good for the Omega and make it last. “How’re you feeling, Cas?” He felt like he had to check in, even as Cas swallowed and nodded. The haze was clearing up slightly by virtue of Dean being there.

“I’m… I’m fine. It still hurts, though.” The pink deepened on his cheeks and went all the way to his chest.

“I’ve got you.” Dean nodded and zipped Castiel’s zipper down and tugged the pants off of Cas, leaving him in tight briefs that had to feel even worse than the boxers. There was barely a bulge, which wasn’t surprising with an Omega, but the way Castiel’s hips seemed to move urged Dean onwards. The back was already wet with slick, and it soaked onto the sheets. His hand stilled Cas’ hips, stroking the skin there. He looked up at Cas and the angel’s glazed over gaze met his. There was an understanding that passed through them, and Dean surged forward again to kiss Castiel as his hands stripped down Castiel’s briefs. Slick pooled as the Omega sighed and moaned in relief, and as one hand of Dean’s brushed against his hole his breath stuttered.

“That’s right, Cas, it’s alright…” He coaxed before a finger pushed in gently. Castiel gave a small cry of surprise and Dean grabbed his hand, lacing their fingers together. “I know, I know… But I’m gonna make you feel good. Do you trust me?”

Castiel nodded, and Dean felt a sudden urge to hold him close. It felt right. Instead, he inserted his finger again, taking his time to stretch the Omega out as he added another finger. Both were thrumming with excitement, but aside from Castiel’s moans and Dean’s quiet praises and affirmations, nothing was said. He made it to three fingers before he deemed Castiel ready enough and took off his own boxers, withdrawing his hand from Castiel’s hole as the other still held his hand. Dean could’ve groaned with relief at letting his aching cock out of its cotton prison, but as soon as he lined himself up with Castiel’s hole, he realized something.

“Cas, I don’t have any protection…” His voice died down a bit, as he tried to speak. Cas barely gave him a look, not even able to muster up a disapproving glare. It was too late to stop now, and he knew if he left Castiel alone, it would spiral downwards and go wrong. So the protest died on his lips, because he was just as eager as Castiel, and neither wanted it to stop.

“I’m ready, Dean. Please.”

That was all it took before Dean did just as the Omega asked. He slid home, and the high cry Castiel gave out and the tightened grip on Dean’s hand almost finished him there.

“ _Shit_ , Cas.” Dean hissed out as he sheathed himself fully. Castiel’s legs wrapped around his waist and Dean began to rock in and out, slowly, but deep with every thrust.

“You feel so good, Alpha.” Castiel’s eyes shined up at Dean, and he allowed himself to get lost in them before they fluttered shut at the sensation. Dean didn’t know where the “Alpha” part came from but damned if it didn’t sound perfect.

Alpha. _Castiel’s_ Alpha.

“You feel perfect, Omega. Perfect and willing just for me…” He hit a sweet spot if judging how Castiel’s back arched and the punched out gasp was any indication.

“Just for you, Dean. Just for you…” Both of them were close, and Dean felt his knot swelling as he went in and out, only slightly picking up speed at Castiel’s request.

“C’mon, Cas… Let go.” Dean finally got out, before his hand touched Castiel’s small cock. It only took a stroke before the Omega let go with a cry of Dean’s name, and Dean followed suit as the knot locked them together. Come splattered against Dean’s chest before the Omega went boneless, and Dean nearly followed. The knot wouldn’t die down for another few hours, and he knew there was going to be a while before the heat kicked in again. But right now, he turned them both on their side, mindful of the lock, and held Cas close as the aftershocks made him shiver. His hand stroked through sweat-damp hair and he pressed a kiss to it.

“Cas? Are you alright? Talk to me.” He wanted to get a read on where Castiel was mentally, if he was asleep or needed to be talked to.

“M’fine, Dean.” It seemed like a mix of both, and Dean wasn’t sure angels could even get tired like the way he sounded. “I’m… embarrassed.” His actions were different from his words, as he seemed to scoot in and cuddle closer to Dean until he was muffled into Dean’s shoulder.

“Embarrassed? Why?” The Alpha asked, with a small bit of concern. He was tired but would fight through it for Castiel.

“To lose myself in such a way… It wasn’t what I’m used to doing.” He admitted quietly. “And to take you into it…”

“Cas, it’s fine.” He forced Castiel to look at him. The look in the Omega’s eyes and the light, shameful blush on his cheeks made Dean sigh slightly. “It’s not wrong. I don’t think any less of you. I… I like it.”

“You like it?” Castiel managed to give him a disbelieving look, despite what else he was feeling.

“I mean that I like taking care of you. And that’s nothing to be ashamed of. You can still be an Angel of the Lord. You can still be Castiel. But…” This time Dean felt his face grow hotter, and he didn’t even know why he was going this far; he was awful with words, especially kind ones, or ones close to his heart that he felt. He didn’t have to say anything, but it had to be a release of hormones and endorphins making him act this way. He took in a breath. “I don’t mind being your mate. Or even just helping you through heats. If… If you want me. But… you’ll still be Castiel. Whether you’re my Omega or not.”

It was silent for a while, and Dean almost regretted not waiting until his knot had died down so he could run or allow Castiel to run if he didn’t want it. Then he felt Castiel kiss him, slowly but sweetly, as his hand ran through Dean’s hair. It was the last thing said for a while.

Three days later, when Castiel’s heat was over, he bared his neck and Dean marked it as his before Castiel did the same to him.

Castiel’s Alpha. Dean’s Omega.

It was right. And it was a beautiful end that led to a beautiful beginning.

**Author's Note:**

> The title is inspired by the King James Version of the Bible:
> 
> I am Alpha and Omega, the beginning and the end. I will give unto him that is athirst of the fountain of the water of life, freely.
> 
> I really only picked it for the first line, lol. But I hope you enjoyed! If you did, please leave me a kudos and/or comment, they make my day! You can also find me at my tumblr castiel-ambrose, where I take requests for other fic you might like! Thank you for stopping by, and have a wonderful day! <3


End file.
